Digital beam displacement circuit

ABSTRACT

A matrix switching system controlled by a code of six fixed digital signals to selectively switch signals energizing two spaced feeds of an antenna array. Five different codes are provided to digitally shift the antenna array beam in five discrete steps.

United Stat GS Patent [191 Burnham' 3,745,580 July 10, 1973 y [75]Inventor:

[54] DIGITAL BEAM DISPLACEMENT CIRCUIT Fred E. Burnliam, Silver Spring,Md.

[73] Assignee: Litton Systems, Inc., College Park,

22 Filed: Apr. 26, 1971 21 Appl. No.: 137,133

[52] US. Cl 343/100 SA, 333/7 D, 343/854 [51] Int. Cl. H011 3/24 [58]Field of Search 343/100 SA, 854,

[56] References Cited UNITED STATES PATENTS 2,688,699 9/1954 fHiehle...343/876X PARALLEL LENS I B N DIGITAL BEAM I STEPPER I l8 l4 2 20 P PLATEINPUT 2,607,008 8/1952 Guarino et a1 333/7 X 3,069,629 l2/l962 Wolff333/7 X 3,l70,l58 2/1965 Rotman 343/100 SA Primary Examiner-Benjamin A.Borchelt Assistant Examiner-Richard E. Berger Att0mey-Alfred B. Levineand Alan C. Rose [5 7] ABSTRACT A matrix switching system controlled bya code of six fixed digital signals to selectively switch signalsenergizing two spaced feeds of an antenna array. Five different codesare provided to digitally shift the antenna array beam in five discretesteps.

10 Claims, 4 Drawing Figures DlVlDER i PATENIEUJUL 1 0 1m SHEET 1 OF 2FIG! DIGITAL BEAM/ STEPPER INVENTOR FRED E. BURNHAM BY e .3. u/liATTORNEY PAIENTEU JUL 1 01973 455 0 SHEEI 8 0F 2 OUTPUT TO l3 LOGIC moveCONDITION OUTPUT 29 2s 27 2s 25 so 12 I3 0N ON I o ON ON 85 58 ON ON ON7 7 on ON 58 a2 ON ON 0 I L} lNVENTOR FRED E. BURNHAM BY 'q f ea8.101418 ATTORNEY 1 DIGITAL BEAM DISPLACEMENT CIRCUIT STATEMENT OF THEINVENTION This invention relates to digitally controlled beam shifting,and is particularly concerned with switching matrices for selectivelyenergizing antenna arrays to shift its beam in descrete angular steps.

BACKGROUND OF THE INVENTION In an-earlier application of Fred E. Burnhamand Williarn H. Clark, of the same assignee, there is disclosed anelectronic digital scanning antenna system capable of scanning a beamabout a full 360 arc in space in a series of small equal steps. Whensuch system is employed in an instrument landing system for aircraft,the beam must be periodically elevated and lowered at different azimuthpositions in its circular scanning path according to the differenttopographical contours of the land surrounding the airport. Thus, forexample, if mountains or hills are located due north of the airport, theradio beam emanating from the airport must be elevated or raised abovethese mountains to guide the aircraft as the scanning beam traverses thedue north azimuth position yet must be again lowered, or tilteddownwardly to follow the land topography as the beam continues itsazimuth scanning over a flat valley located due west, for example, fromthe airport.

Briefly, according to the present invention there is provided adigitally controlled switching matrix for rapidly and precisely shiftingor tilting the beam from an antenna array between a lower and upperangular position, or to any one or more of plural intermediatepositions, all as controlled by a code of six digital signals applied tothe matrix.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematic drawingillustrating a preferred antenna array system and a digitally controlledbeam stepper, 1

FIG. 2 is an elevation polar plot of the beam components produced by thesystem of FIG. 1,

FIG. 3 is an electrical schematic drawing of a preferred digital steppermatrix according to the invention, and

FIG. 4 is a tabulation of the logic signals applied to control thedigital stepper and the output of the stepper.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 illustrates an antennaarray that may be employed in combination with a digital beam stepper 17of the present invention to provide a beam that can be angularlydisplaced or stepped in a series of descrete angular increments.

As shown, the preferred array comprises a parallel plate lens 10 in theform of a pair of large spaced apart plates having a hemisphericalcontour or periphery. A series of radiating elements 11, energized bycables or transmission lines, are connected at equally spaced apartlocations about the hemispherical contour. To enable the array toproduce a plane wavefront beam with equal phasing from all of theradiating elements 11-, the feed cable lengths are progressivelylengthened, for those cable feeds above and below the horizontal center,to provide a progressive 44 degree phase shift at the frequencyinvolved. The parallel plate lens 10 is provided with five spaced apartfeed probes 12, 13, 14,

15, and 16, along its diameter as shown, that are spaced apart in apreselected manner to provide the angularly spaced apart beams shown inFIG. 2. As shown, where only probe 12 is energized, the lowermost beam,similarly numbered as 12 in FIG. 2 is provided. In a similar manner eachof the other beams 13, 141, 15, and 16 are produced when the similarlynumbered probe of the lens is energized. When more than one probe isenergized, the beam produced by the array comprises the algebraic sum ofthe individual beams.

It will be appreciated by those skilled in the art that both theindividual amplitudes and phases of the signals applied to the variousprobes may be varied to change the waveshape and spatial position of thebeam.

For applying a given fixed amplitude distribution of signals to theprobes, so as to provide a beam of given waveshape, an input signal 23is initially applied to a fixed power divider 18 having four outputlines 19, 20, 21, and 22. In a preferred embodiment, power divider 18divides the signal to provide the following amplitude distribution ofsignals on these lines:

Relative Line Amplitude 19 1.0 20 0.8 21 0.8 22 1.3

For rapidly stepping the beam upwardly or downwardly through a series ofdifferent angular positions, the signal on line 19 is directed by theadjustable digital stepper 17 to be applied to either probe 12 or toprobe 13, or is apportioned in amplitude between both probes, all asshown in the tabulation of FIG. 1.

For example, when the entire signal on line 19 is applied to probe 12and probe 13 is deenergized, the resulting beam, comprisingthe algebraicsum of beams 16, 15, 14, and 12 is tilted downwardly to its lowermostspatial position. Similarly when the: entire signal on line 19 isapplied to probe 13 and probe 12 is deenergized, beams 13, M, 15, and 16are sumed and the resulting beam is tilted to its upper most position.For any intermediate division of power between the two probes 12 and 13the resulting beam is tilted at an angle intermediate these two angularpositions.

FIG. 3 illustrates a preferred vertical beam stepper matrix 17,according to the invention, for providing five descrete angular steps ofthe beam as controlled by a digital code of signals.

As shown, the digitally controlled matrix includes a number of pairs ofseries connected transmission lines interconnecting the input line 19with each of the output lines leading to probes 12 and 13. A first pairof such lines 41) and 41 end at cross-over junction 60, and a secondpair of lines 44 and 4 5 begin at junction 60 and terminate at theoutput to probe 12. In parallel with the first pair of line 40 and 11 isa third series connected pair 12 and 43; and in parallel with the secondpair of lines 44 and 45 is a fourth series connected pair 46 and 47. Ina similar manner, a fifth pair of lines 48 and 49 interconnect thecrossover junction 60 with the output leading to probe 13, and a sixthpair of lines 50 and 51 parallel the fifth pair. At each junction of theseries connected pairs there is provided a biased diode, includingdiodes 25 to 30, inclusive, that serve to selectively connect thatjunction to ground when properly energized.

Each of the transmission lines 40 to 51 in the matrix is one quarterwavelength long at the high frequency of the signal, and each has a veryhigh input impedance with the biased diode in one condition, off, toblock passage of the signal but a different, much lower, finiteimpedance for transmission of the signal therethrough when the diode isenergized to its on. condition.

In operation, by selectively energizing different groups of diodes in agiven logic pattern, the input signal is selectively directed to eitheroutput 12 or 13 or is apportioned in given ratios between both outputs.This logic is shown in FIG. 4.

For example, referring to FIGS. 3 and 4, when diodes 28 and 26 areenergized to on" condition, the input signal from 19 passes only throughlines 40, 41, 46, and 47 to the output leading to probe 12 and no signalis permitted to pass through to the output. leading to probe 13. On theother hand where diodes 25, 26, and 29 are on and all others are off,the input signal passes throughlines 42 and 43, reaching the cross-overjunction 60, and thence splits with a portion traveling over lines 46and 47 to output 12 and the remaining portion over lines 50 and 51 tooutput 13. Due to the fixed relationships of the different impedences ofthese branching lines, an amplitude of 0.82 of the signal is directed toprobe 13. This mode of energization steps up thebeam by one increment orstep from its lowest position when only probe 12 is energized and probe13 is deenergized. In a similar manner it can be shown that by applyingeach other one of the logic codes shown in F IG .4 to energize theappropriate diodes, the-beam can be stepped to any other of theotherfive angular positions. I

It will be noted that any one of the angular steps may be selectedwithout passing through 'the previous steps, and the described matrixpermits a preselection of the desired beam angle at any one of sixdifferent angles. Thus when the system is employed in an instrumentlanding system to scan over an abrupt change of terrain, passing, forexample, a precipitous cliff, the beam may be abruptly stepped or tiltedfrom its lowest position with diodes 26 and 28 on" to its highestposition by energizing diodes 28 and 30 to on.

Although the antenna system and matrix have been described as a signaltransmitting array with an input signal applied to the powerdivider 18,it is believed evident that the described components may be reciprocaldevices'that pass signals in the reverse direction and accordinglyprovide a digitally controlled directional scanning receiver. Sinceother variations may be made without departing from the invention, thisinvention is to be considered as limited only by the following claims.

What is claimed is:

l. A high frequency switching matrix having an input, a pair of outputsand digitally operating means for selectively apportioning a signal atthe input to either output and apportioning an input signal between bothoutputs in different fixed proportions, said matrix including aplurality of pairs of high frequency transmission lines interconnectingsaid input and both outputs, each line being one quarter wavelength inlength, energizable switching means at the junction of each of saidlected impedance when said switching means is energized in anothercondition; finite preselected impedances of said lines being apportionedaccording to the desired apportionment of signals between said outputs,and means selectively applying energization to different groups of lessthan all of said energizable switching means.

2. In the matrix of claim 1, at least two pairs of series connectedtransmission lines interconnecting the input and each output.

3. In the matrix of claim 2, at least two additional pairs of seriesconnected transmission lines interconnecting the input and each of theoutputs with the addi tional pairs being in parallel with the firstmentioned pairs.

4. In the matrix of claim 1, two pairs of series connected transmissionlines interconnecting said input and each output with said switchingmeans at the junction of each said pairs, and said two pairs meeting ata common crossover junction.

5. In the matrix of claim 4, at least two additional pairs of seriesconnected transmission lines, with the additional pairs in parallelrelation to the first menpairs of transmission lines for selectivelygrounding said junctions thereby to selectively apply a very highimpedance at the input of that pair of lines when said switch isenergized in one condition and a finite presetioned pairs.

6. in combination with the switching matrix of claim 1, an antenna arrayhaving a plurality of energizable probes with two of said probesenergizable by the pair of outputs of said matrix, whereby the beamprovided by the antenna array is stepped in angular position uponapplication of digital energization to different groups of said means.

7. In the matrix of claim 1, a cross over junction a first pair of saidtransmission lines interconnecting said input and cross over junction, asecond pair of said transmission lines in parallel with said first pair,a third pair of transmission lines interconnecting said crossoverjunction and one of said outputs, a fourth pair of said lines inparallel with said third pair, a fifth pair of said linesinterconnecting said cross-over junction and said other output, a sixthpair of said lines in parallel with said fifth pair, energizable backbiased diodes at the interconnection of each pair of lines andselectively energizable to ground said junction, the open circuitimpedances of said first pair being 50 ohms and 59 ohms, respectively;the open circuit impedances of said second pair being 50 ohms and 45.4ohms respectively; the open circuit impedances of the third pair being59 ohms and 50 ohms respectively, the open-circuit impedances of saidfourth pair being 83.6 ohms and 50 ohms, respectivelyythe open circuitimpedances of said fifth pair being 83.6 ohms and 50 ohms, respectively;and the open circuit impedances of said sixth pair being 59 ohms and 50ohms respectively.

8. In the matrix of claim 7, means selectively digitally energizing theback biased diodes to ground the junction ofthe first pair and thirdpair thereby to selectively interconnect the input and only one output,and means selectively energizing the back biased diodes to ground thejunction of the first pair and the sixth pair thereby to selectivelyinterconnect the input and only the other output.

9. An electronic beam forming and electronic beam tilting systemcomprising:

an antenna array having a plurality of spaced antenna elements and aplurality of assymmetrically disposed feed means with each feed meansenergizing all antenna elements,

each of said feed means providing a beam component from said antennaelements that is angularly displaced ahead of an adjoining beamcomponent produced by a different one of said feed means, whichdifferent one is in turn, angularly displaced ahead of a still differentone of said feed means, thereby to provide a series of successivelydisplaced beam components, I

and means for electronically tilting said beam,

1. A high frequency switching matrix having an input, a pair of outputsand digitally operating means for selectively apportioning a signal atthe input to either output and apportioning an input signal between bothoutputs in different fixed proportions, said matrix including aplurality of pairs of high frequency transmission lines interconnectingsaid input and both outputs, each line being one quarter wavelength inlength, energizable switching means at the junction of each of saidpairs of transmission lines for selectively grounding said junctionsthereby to selectively apply a very high impedance at the input of thatpair of lines when said switch is energized in one condition and afinite preselected impedance when said switching means is energized inanother condition; finite preselected impedances of said lines beingapportioned according to the desired apportionment of signals betweensaid outputs, and means selectively applying energization to differentgroups of less than all of said energizable switching means.
 2. In thematrix of claim 1, at least two pairs of series connected transmissionlines interconnecting the input and each output.
 3. In the matrix ofclaim 2, at least two additional pairs of series connected transmissionlines interconnecting the input and each of the outputs with theadditional pairs being in parallel with the first mentioned pairs.
 4. Inthe matrix of claim 1, two pairs of series connected transmission linesinterconnecting said input and each output with said switching means atthe junction of each said pairs, and said two pairs meeting at a commoncrossover junction.
 5. In the matrix of claim 4, at least two additionalpairs of series connected transmission lines, with the additional pairsin parallel relation to the first mentioned pairs.
 6. In combinationwith the switching matrix of claim 1, an antenna array having aplurality of energizable prObes with two of said probes energizable bythe pair of outputs of said matrix, whereby the beam provided by theantenna array is stepped in angular position upon application of digitalenergization to different groups of said means.
 7. In the matrix ofclaim 1, a cross over junction, a first pair of said transmission linesinterconnecting said input and cross over junction, a second pair ofsaid transmission lines in parallel with said first pair, a third pairof transmission lines interconnecting said cross-over junction and oneof said outputs, a fourth pair of said lines in parallel with said thirdpair, a fifth pair of said lines interconnecting said cross-overjunction and said other output, a sixth pair of said lines in parallelwith said fifth pair, energizable back biased diodes at theinterconnection of each pair of lines and selectively energizable toground said junction, the open circuit impedances of said first pairbeing 50 ohms and 59 ohms, respectively; the open circuit impedances ofsaid second pair being 50 ohms and 45.4 ohms respectively; the opencircuit impedances of the third pair being 59 ohms and 50 ohmsrespectively, the open circuit impedances of said fourth pair being 83.6ohms and 50 ohms, respectively; the open circuit impedances of saidfifth pair being 83.6 ohms and 50 ohms, respectively; and the opencircuit impedances of said sixth pair being 59 ohms and 50 ohmsrespectively.
 8. In the matrix of claim 7, means selectively digitallyenergizing the back biased diodes to ground the junction of the firstpair and third pair thereby to selectively interconnect the input andonly one output, and means selectively energizing the back biased diodesto ground the junction of the first pair and the sixth pair thereby toselectively interconnect the input and only the other output.
 9. Anelectronic beam forming and electronic beam tilting system comprising:an antenna array having a plurality of spaced antenna elements and aplurality of assymmetrically disposed feed means with each feed meansenergizing all antenna elements, each of said feed means providing abeam component from said antenna elements that is angularly displacedahead of an adjoining beam component produced by a different one of saidfeed means, which different one is in turn, angularly displaced ahead ofa still different one of said feed means, thereby to provide a series ofsuccessively displaced beam components, and means for electronicallytilting said beam, said tilting means comprising electronic switchingmeans for adjustably apportioning the amplitude of energy between a pairof said feed means producing adjoining beam components.
 10. In thesystem of claim 9, said switching means being digitally controlled insteps to provide a plurality of descrete angular tilt levels.